There is a fundamental gap in understanding how best to use movement to minimize spasticity and maximize function and quality of life in people with MS. It is important to address this gap because spasticity is the most prevalent cause of neurological disability in young adults, and therapeutic options for people with MS are limited. Our long-term goal is to understand how neuroplasticity in people with MS can be exploited to improve function and quality of life. The objective of this application is to determine if downslop walking (DSW) as a functional movement changes spinal excitability as a measure of the underlying circuitry explaining neuroplasticity and sensorimotor function in MS. The central hypothesis is that DSW training will reduce spinal excitability and spasticity with a possible long term outcome of sustaining or improving walking ability in people with MS, in whom neural lesions negatively impact movement. This hypothesis has been formulated based on preliminary studies in the applicant's laboratory. The rationale for this research is that understanding how to tailor exercise training to target neuroplasticity is a necessary step in the development of strategies to stabilize or reverse disease progression and improve quality of life for people suffering from MS. Guided by preliminary data, this hypothesis will be testing by pursuing two specific aims: 1) Compare the effects of downslope, upslope and level treadmill walking on spinal excitability and ankle clonus in people with MS, and 2) Compare the effects of downslope, upslope and level treadmill walking on presynaptic inhibition in people with MS. A proven protocol established in the applicant's lab will be used to address these aims. H- reflexes and clonus will be measured while subjects are at rest, before and twice after 20 minutes of treadmill walking (at 10 min's and 45 min's post) during three visits. On one day the treadmill wil not be inclined, on another day the treadmill will be set at -7.5%, and on another day it will be set at +7.5%. The approach is innovative because it uses an inexpensive and accessible model of exercise based on promising evidence that it evokes spinal plasticity in a way that could benefit people with MS. The proposed pilot research is significant because it is expected to vertically advance and expand the understanding of how to tailor exercise to the specific needs of people with MS. Ultimately, this knowledge has the potential to inform the development of better exercise interventions that will help increase quality of life in people with MS.